Valeooscope - Air Conditioning System Thermal comfort loop

11.1.5 Suction pressure limits Increasing the fluid suction reduces the pressure inside the evaporator. g Too low a pressure would generate too low a temperature at the evaporator surface and a risk of freezing. g Freezing at evaporator surface would block the air flow, jeopardising heat exchanges and thus the fluid evaporation. g This would lastly put the compressor in danger, as it could digest liquid refrigerant via the suction port.

11.1.4 The suction level The compressor suction level establishes the fluid phase change conditions inside the evaporator; this is a crucial parameter for heat exchange and cooling performance. The suction pressure (low pressure of the A/C loop) is initiated by the compressor to ensure the appropriate evaporation process inside the evaporator (not less than 3 bars for R134a refrigerant). Less compressor suction implies: g Higher evaporator pressure, thus higher refrigerant boiling temperature g Higher evaporator temperature g Reduced thermal exchanges with the ambient air More compressor suction implies: g Lower evaporator pressure, thus lower refrigerant boiling temperature g Lower evaporator temperature g Increased thermal exchanges with the ambient air Control of the suction level:

Absolute pressure (bar)

Boiling Temp. R134a (°C)

1,57 1,71 1,85 2,01 2,17 2,34 2,53 2,72 2,93 3,15 3,38 3,62 3,88 4,43 5,04 5,72 6,46

-16 -14 -12 -10

Suction pressure forbidden zone

Evaporator freezing

-8 -6 -4 -2

0 2 4 6 8

3 bars

Cooling capacity control

Working zone

12 16 20 24

AC High pressure (HP)

A/C Low pressure (LP)

Condenser

Compressor Suction port

Receiver drier

Evaporator

Expansion valve

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